RHR1K160D Datasheet, PDF (5/9 Pages) Intersil Corporation – 1A, 600V Hyperfast Dual Diode

RHR1K160D
Thermal Resistance vs Mounting Pad Area
The maximum rated junction temperature, T_JM, and the
thermal resistance of the heat dissipating path determines
the maximum allowable device power dissipation, P_DM, in an
application. Therefore the application’s ambient temperature,
T_A (^oC), and thermal resistance R_θJA (^oC/W) must be
reviewed to ensure that T_JM is never exceeded. Equation 1
mathematically represents the relationship and serves as
the basis for establishing the rating of the part.
P_DM = -⁽--^T----^J-_Z--^M--_θ----_J^–---_A-^T----^A----⁾
(EQ. 1)
In using surface mount devices such as the SOP-8 package,
the environment in which it is applied will have a significant
influence on the part’s current and maximum power
dissipation ratings. Precise determination of P_DM is complex
and influenced by many factors:
1. Mounting pad area onto which the device is attached and
whether there is copper on one side or both sides of the
board.
2. The number of copper layers and the thickness of the
board.
3. The use of external heat sinks.
4. The use of thermal vias.
5. Air flow and board orientation.
6. For non steady state applications, the pulse width, the
duty cycle and the transient thermal response of the part,
the board and the environment they are in.
Intersil provides thermal information to assist the designer’s
preliminary application evaluation. Figure 13 defines the
R_θJA for the device as a function of the top copper
(component side) area. This is for a horizontally positioned
FR-4 board with 2 oz. copper after 1000 seconds of steady
state power with no air flow. This graph provides the
necessary information for calculation of the steady state
junction temperature or power dissipation. Pulse
applications can be evaluated using the Intersil device
SPICE thermal model or manually utilizing the normalized
maximum transient thermal impedance curve.
350
R_θJA = 110.2 - 25.24 x ln (AREA)
300
239^oC/W - 0.006in²
250
201^oC/W - 0.027in²
200
150
100
R_θβ = 43.81 - 22.66 x ln (AREA)
50
0.001
0.01
0.1
AREA, TOP COPPER AREA (in²)
FIGURE 13. THERMAL RESISTANCE vs MOUNTING PAD AREA
Displayed on the curve are R_θJA values listed in the
Electrical Specifications table. These points were chosen to
depict the compromise between the copper board area, the
thermal resistance and ultimately the power dissipation,
P_DM. Thermal resistances corresponding to other
component side copper areas can be obtained from Figure
13 or by calculation using Equation 2. The area, in square
inches is the top copper board area, the thermal resistance
and ultimately the power dissipation, P_DM.
R_θJA = 110.18 – 25.24 × ln (Area)
(EQ. 2)
While Equation 2 describes the thermal resistance of a
single die, the dual die SOP-8 package introduces an
additional thermal component, thermal coupling resistance,
R_θβ. Equation 3 describes R_θβ as a function of the top
copper mounting pad area.
R_θβ = 43.81 – 22.66 × ln (Area)
(EQ. 3)
The thermal coupling resistance vs. copper area is also
graphically depicted in Figure 13. It is important to note the
thermal resistance (R_θJA) and thermal coupling resistance
(R_θβ) are equivalent for both die. For example at 0.1 square
inches of copper:
R_θJA1 = R_θJA2 = 168^oC/W
R_θβ1 = R_θβ2 = 96^oC/W
T_J1 and T_J2 define the junction temperature of the
respective die. Similarly, P₁ and P₂ define the power
dissipated in each die. The steady state junction
temperature can be calculated using Equation 4 for die 1
and Equation 5 for die 2.
Example: Use Equation 4 to calculate T_J1 and Equation 5 to
calculate T_J2 with the following conditions. Die 2 is
dissipating 0.5W; die 1 is dissipating 0W; the ambient
temperature is 60^oC; the package is mounted to a top
copper area of 0.1 square inches per die.
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